The　effects　of　four　swirl　ratios　of　0.4,　0.6,　0.8　and　1.0　and　three　density　ratios　of　1.0,　1.5　and　2.0　in　the　upstream　slot　jet　flow　with　preswirl　on　the　turbine　endwall　cooling　and　suction　surface　phantom　cooling　performance　are　numerically　investigated　using　the　three-dimensional　Reynolds-averaged　Navier-Stokes　(RANS)　equations　and　the　SST　turbulent　model.　The　computational　model　of　the　turbine　endwall　taking　into　account　the　upstream　slot　jet　flow,　the　film　cooling　on　the　endwall　surface　and　the　gap　in　the　cascade　passage　is　taken　as　the　analysis　objective.　The　results　indicate　that　at　a　low　density　ratio,　decreasing　the　swirl　ratio　of　the　slot　jet　flow　has　a　negative　effect　on　the　endwall　cooling　effect.　At　a　high　density　ratio,　the　cooling　effect　first　decreases　and　then　increases,　with　the　minimum　value　appearing　at　the　swirl　ratio　of　0.8.　The　density　ratio　has　a　negative　effect　on　the　cooling　performance,　and　the　position　of　the　lowest　effect　moves　downstream　with　the　swirl　ratio.　By　reducing　the　relative　motion　of　the　coolant　and　rotor,　the　phantom　cooling　coverage　of　the　slot　jet　flow　becomes　smaller　and　moves　downstream,　close　to　the　endwall,　which　results　in　a　lower　phantom　cooling　effect.　Increasing　the　density　ratio　of　the　coolant　results　in　a　smaller　phantom　cooling　coverage　which　moves　to　the　endwall,　hence　reducing　the　phantom　cooling　effect　on　the　blade　suction　surface.　©　2018,　Editorial　Office　of　Journal　of　Xi＇an　Jiaotong　University.　All　right　reserved.